In a commercially available pressure regulating system, pressure in a jacket surrounding a flexible tube is maintained at a level to prevent radial stretching of the tube for fluid flow as long as the monitored pressure in the pipeline is at the desired level. However, should the pressure in the pipeline being monitored deviate from that level, i.e. deteriorate where it is the pressure downstream of the valve that is being monitored, the jacket pressure is evacuated to enable the valve to open. Such evacuation is under control of a pilot valve wherein the pressure being monitored acts against a diaphragm in opposition to an adjusted spring force. Hence, should the spring force overcome the monitored pressure acting against the diaphragm, the pilot valve is opened and the chamber or jacket is evacuated. Then, when the desired pressure is again reached, the spring is overcome to close the pilot valve and allow the jacket pressure to build up again.
In practice, the system just described has proven highly satisfactory for most pressure control services. However, in some applications, as when seeking fine control at low pressure, difficulty has been experienced in maintaining stability of the sensitive pilot valve, resulting in valve chattering.